Apparatus and method for producing liquid oxygen and/or liquid nitrogen by low temperature rectification of atmospheric air



March 1, 1966 J. MEISLER 3,237,418

APPARATUS AND METHOD FOR PRODUCING LIQUID OXYGEN AND/OR LIQUID NITROGEN BY LOW TEMPERATURE RECTIFICATION OF ATMOSPHERIC AIR Filed Oct. 26, 1960 OXYGEN PRODUCT LIQUID REF LUX COLUMN PRV 6 OXYGEN JOSEPH MEISLER BY W 1?. AGE T AIR FEED United States Patent APPARATUS AND METHOD FOR PRODUCING LIQUID OXYGEN AND/0R LIQUID NITROGEN BY LQW TEWERATURE RECTIFICATION OF ATMOSPHERIC AIR Joseph Meisler, New York, N.Y., assignor to North American Philips Company, Inc., New York, N .Y., a corporation of Delaware Filed Oct. 26, 1960, Ser. No. 65,023 5 Claims. (Cl. 6214) This invention relates to a process and apparatus for producing liquid oxygen and/or liquid nitrogen by low temperature rectification of atmospheric air.

It is an object of the present invention to provide an apparatus for producing liquid oxygen which uses a low pressure air separation cycle requiring 70 to 90 p.s.i.g. air feed pressure.

It is another object of the present invention to provide an installation for producing liquid oxygen and/or liquid nitrogen which occupies a minimum of space with regard to overall height. Thus, the present installation is of special advantage when mounting in confined spaces is required.

It is still another object of the present invention to provide an apparatus for producing liquid oxygen in which no internal mechanical or thermal pumping of reflux or products is required since all fluids flow progressively from the compressor head pressure to reduced pressure waste streams, product streams, or reflux streams.

Another object of the present invention is the provision for removing all moisture and carbon dioxide from the air supply to the installation without the use of conventional chemical agents or auxiliary equipment.

It is a further object of the present invention to provide an apparatus for producing liquid oxygen and/or liquid nitrogen in which the required refrigeration is supplied at optimum efliciency and the apparatus is flexible in controlling the capacity of the cycle and the distribution and purity of its products. Thus, the cycle would be suitable for producing varying quantities of high purity liquid nitrogen simultaneously with the production of high purity liquid oxygen product.

It should be apparent that the low pressure cycle of the present invention has the ability to control efliciently the required refrigeration of the plant. Its low operating pressure permits the use of an efficient and economical heat exchanger surface and reduces the hazard of hydrocarbon contamination of the products by the feasi bility and use of an oil free compressor and an eflicient liquid phase adsorber.

It should be apparent that the present process becomes self cleaning and continuous in operation for long periods of time.

The above and other features, objects and advantages of the present invention will be fully understood from the following description considered in connection with the accompanying illustrative drawing.

In order to carry out the present invention it will now be described in detail with reference to the accompanying diagram of and sole figure the cycle of the apparatus constructed in accordance with the present invention.

The following is a glossary of abbreviations used in the sole figure of the drawing:

FI-Flow Indicator RVRelief Valve LLi-Liquid Level Indicator PD-Pressure Difference Meter P-Pressure Meter (Manometer) PRVPressure Reducing Valve LLCLiquid Level Control SVSafety Valve Referring more particularly to FIGURE 1, atmospheric air is drawn into air compressor 14 wherein it is compressed to about 70 p.s.i.g. pressure. One fraction of the compressed air from compressor 14 is then led through section C of unbalanced reversing type seetional heat exchanger 16, where it is cooled below minus 260 F. by the total efliuent waste streams passing in the opposite direct-ion in section 16a of heat exchanger 16 and consisting of the overhead vapors from liquid oxygen column 18 and cold vapors from condenser 22 of the nitrogen column 20, that have been warmed in heat exchanger 50 to a temperature slightly above the dew point temperature of the airfeed by the warm air efliuent from unbalanced pass 16b of heat exchanger 16, and conducted to exchanger 56 and section 16a by means of line 21.

The remaining air from compressor 14 is led through refrigerated filter 23 where it is cleaned of CO and moisture and cooled below minus 260 F. by boiling bottoms from nitrogen column 20. A fraction of the combined cold air streams leaving filter 23, section of the heat exchanger 16 and heat exchanger 50 is fed to nitrogen column 20 through line 23 wherein it is rectified into a high purity nitrogen vapor overhead and a rich liquid air bottom. The overhead nitrogen vapors from column 21) are condensed in cold gas refrigerator 26 and transferred to surge tank 28 for use as a liquid reflux to oxygen column 18 as well as other refrigeration requirements and/or product.

The residual cold air not fed to column 20 is conducted through line 19 and condensed in reboiler 30 of oxygen column 18, the heat of condensation generated providing the boil-up energy of rectification in said oxygen column 18. The liquid air produced in reboiler 30 is combined via line 49 with control rich liquid air bottoms from nitrogen column 20, and after being cleaned of dissolved atmospheric hydrocarbon contaminants in adsorber 32 and after being cooled in cycle air subcooler 38 by the combined gas streams from condenser 22 and overhead from column 18, it is passed at reduced pressure into nitrogen column condenser 22 to provide the required refrigeration therein for producing the necessary internal reflux for column 20. The evaporated liquid air in condenser 22 is combined with overhead vapors from column 18 at point 25 and warmed in cycle air subcooler 33 and thence passed through heat exchangers 50 and 16, as described above.

The rich liquid air bottoms from nitrogen column 20 are cleaned in adsorber 40, and thereafter subcooled in cooler 34 by boiling liquid nitrogen made available from surge tank 28. The cooled, rich liquid air, entering oxygen column 18 at reduced pressure as a saturated liquidvapor mixture is rectified therein into liquid oxygen product bottoms of at least 99.5% purity. The overhead vapors from column 18 are mixed with the cold vapors of nitrogen condenser 22 to provide the refrigeration for reversing heat exchange 16 as described above.

The liquid oxygen product is withdrawn from column 18 at 44 after traversing cooler 34 where its temperature is reduced to about minus 300 F. by boiling liquid nitrogen. The foregoing low temperature has the desirable effect of eliminating liquid flash during transfer to a vented liquid oxygen storage tank (not shown).

The liquid nitrogen product is Withdrawn from surge tank 28 and tapped off at 46 and/or 48.

While I have shown and described the preferred embodiment of my invention, it will be understood that the latter may be embodied otherwise than as herein specifically illustrated or described and that in the illustrated embodiment certain changes in the details of construction and in the arrangement of parts may be made without departing from the underlying idea or principle of the invention within the scope of the appended claims.

What I claim is:

1. An apparatus for selectively producing liquid oxygen and liquid nitrogen by low temperature rectification of atmospheric air with the use of a reversing type sectional heat exchanger comprising a compressor for compressing said atmospheric air to about 70 p.s.i.g. pressure, a nitrogen rectifier column for the air stream from the reversing type heat exchanger producing nitrogen vapors and liquid air bottoms, a liquid oxygen column producing a liquid oxygen product from said liquid air bottoms, said reversing type sectional heat exchanger for the compressed air being in heat exchanging contact with a waste return gas stream from said oxygen and nitrogen columns passing in the opposite direction, a cold gas refrigerator for condensing the nitrogen vapors drawn off from said nitrogen column to form a liquid nitrogen product, and a subcooler in which a first part of said liquid nitrogen product is received therein for indirect heat exchange with said liquid oxygen product and a second part of said liquid nitrogen product, the said second part being used as a liquid reflux for said oxygen column, the liquid oxygen product being also traversed through said subcooler and withdrawn therefrom in a subcooled state, and the liquid nitrogen vapors in said subcooler being conducted off to said waste return stream from said liquid oxygen column.

2. An apparatus for selectively producing liquid oxygen and liquid nitrogen by low temperature rectification of atmospheric air with the use of a reversing type sectional heat exchanger comprising a compressor for compressing said atmospheric air to about 70 p.s.i.g. pressure, a nitrogen rectifier column producing nitrogen vapors and liquid air bottoms, from the air stream drawnfrom the reversing heat exchanger said nitrogen rectifier column being provided with a reflux condenser, a liquid oxygen column producing a liquid oxygen product from said liquid air bottoms, a reboiler in heat exchange with the liquid air bottoms in the liquid oxygen column to liquify a portion of compressed air drawn from the reversing heat exchanger, said reversing type sectional heat exchanger for the compressed air being in heat exchange contact with a waste return gas stream from said oxygen and nitrogen columns passing in the opposite direction, a cold gas refrigerator for condensing the nitrogen vapors drawn off from said nitrogen column to form said liquid nitrogen product whereas said liquid nitrogen is used as a liquid reflux for said oxygen column, a subcooler whereby said liquid air bottoms are traversed therethrough and the liquid oxygen product is also traversed therethough in heat exchange relationship with said liquid nitrogen, said liquid oxygen being withdrawn from said subcooler, and the compressed air liquefied in said reboiler of said oxygen column acting as the refrigeration source for said reflux condenser of said nitrogen column.

3. A method for selectively producing liquid oxygen and liquid nitrogen products by low temperature rectification of atmospheric air in a nitrogen rectifier column and a liquid oxygen column utilizing a sectional heat exchanger and refrigerated filters in said system and a liquid nitrogen subcooler comprising the steps of compressing atmospheric air; conducting a fraction of said compressed air through said reversing type sectional heat exchanger where it is cooled below minus 260 F. by a combined waste return gas stream from the liquid oxygen and nitrogen rectifier columns passing in the opposite direction, cooling the compressed air present in said refrigerated filters through boiling of nitrogen column bottoms; passing the air stream to the nitrogen rectifying column to form the said nitrogen column bottoms enriched in oxygen to a liquid oxygen column, condensing the nitrogen vapors from said nitrogen column in a cold gas refrigerator and using a first part of the condensate as a liquid nitrogen reflux to said liquid oxygen column through a second part of said condensate as boiling nitrogen subcooler, withdrawing the remainder of said condensate as a liquid nitrogen product, further withdrawing a liquid oxygen product from the bottom of said oxygen column and passing through said liquid nitrogen subcooler, and conducting off the liquid nitrogen vapors in said subcooler to the waste return stream from said liquid oxygen column.

4. A method for selectively producing liquid oxygen and liquid nitrogen products by low temperature rectification of atmospheric air in a nitrogen rectifier column and a liquid oxygen column utilizing a reversing sectional heat exchanger and refrigerated filters in said system and a liquid nitrogen subcooler comprising the steps of compressing atmospheric air; conducting a fraction of said compressed air through said reversing type sectional heat exchanger where the compressed air is cooled below 260 F. by a combined waste return gas stream from said liquid oxygen column' and said nitrogen rectifier column passing in the opposite direction; cooling said compressed air in said refrigerated filters through boiling of nitrogen column bottoms; from the air stream drawn from the reversing heat exchanger condensing the nitrogen vapors from said nitrogen column in a cold gas refrigerator and using a first part of the condensate as a liquid reflux to the top of said oxygen column, utilizing a second part of said condensate in the liquid nitrogen subcooler, and withdrawing the remainder of said condensate as the liquid nitrogen product, and further withdrawing the liquid oxygen product from the bottom of said oxygen column as subcooled liquid through said liquid nitrogen subcooler.

5. A method for selectively producing liquid oxygen and liquid nitrogen products as claimed in claim 3 further comprising cooling and purifying a fraction of said compressed air in said reversing type heat exchanger, and controlling such purity by cooling the residual fraction of compressed air in said refrigerated filter maintained at a temperature less than minus 275 F. by the nitrogen vapors of said nitrogen rectifier and by the boiling nitrogen column bottoms from said nitrogen rectifier column.

References Cited by the Examiner UNITED STATES PATENTS 1,211,125 1/1917 Fonda 6229 X 1,607,323 11/1926 Van Nuys 6229 X 2,113,680 4/1938 De Baufre 6219 X 2,386,297 10/1945 Dennis 6214 X 2,406,003 8/ 1946 Dennis 62-29 X 2,409,458 10/ 1946 Van Nuys 6226 2,500,136 3/1950 Ogerzaly 6229 X 2,729,953 1/1956 Schilling 6215 X 2,729,954 1/ 1956 Etienne 62--31 X 2,753,698 7/1956 Jakob 6214 X 2,802,349 8/1957 Skaperoas 6214 2,824,428 2/ 1958 Yendall 62-29' X 2,850,880 9/1958 Jakob 6229 2,875,587 3/1959 Vanderster 6240 2,932,174 4/1960 Schilling 62--13 2,955,434 10/1960 Cost 62-l3 2,959,021 11/1960 Grenier 6229 2,982,107 5/ 1961 Smith 6229 X FOREIGN PATENTS 1,215,438 11/1959 France.

NORMAN YUDKOFF, Primary Examiner,

RICHARD A. OLEARY, Examiner. 

3. A METHOD FOR SELECTIVELY PRODUCING LIQUID OXYGEN AND LIQUID NITROGEN PRODUCTS BY LOW TEMPERATURE RECTIFICATION OF ATMOSPHERIC AIR IN A NITROGEN RECTIFIER COLUMN AND A LIQUID OXYGEN COLUMN UTILIZING A SECTIONAL HEAT EXCHANGER AND REFRIGERATED FILTERS IN SAID SYSTEM AND A LIQUID NITROGEN SUBCOOLER COMPRISING THE STEPS OF COMPRESSING ATMOSPHERIC AIR; CONDUCTING A FRACTION OF SAID COMPRESSED AIR THROUGH SAID REVERSING TYPE SECTIONAL HEAT EXCHANGER WHERE IT IS COOLED BELOW MINUS 260*F. BY A COMBINED WASTE RETURN GAS STREAM FROM THE LIQUID OXYGEN AND NITROGEN RECTIFIER COLUMNS PASSING IN THE OPPOSITE DIRECTION, COOLING THE COMPRESSED AIR PRESENT IN SAID REFRIGERATED FILTERS THROUGH BOILING OF NITROGEN COLUMN BOTTOMS; PASSING THE AIR STREAM TO THE NITROGEN RECTIFYING COLUMN TO FORM THE SAID NITROGEN COLUMN BOTTOMS ENRICHED IN OXYGEN TO A LIQUID OXYGEN COLUMN, CONDENSING THE NITROGEN VAPORS FROM SAID NITROGEN COLUMN IN A COLD GAS REFRIGERATOR AND 